The present application claims priority to Japanese Application No. P10-219216 filed Aug. 3, 1998 and Japanese Application No. P11-037471 filed Feb. 16, 1999, which applications are incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to an electrical connecting device and an electrical connecting method for electrically connecting an electrical connecting portion of a first object to an electrical connecting portion of a second object.
2. Description of the Related Art
With recent smaller sized and decreased thickness of electronic parts, circuits for use therein have been denser and more precise, so that connection of such an electronic part to a fine electrode is difficult with conventional soldering method, rubber connector or the like. Therefore, adhesive agent and film material (hereinafter referred to as connecting member) having anisotropy excellent in fine pitching and conductivity have been often used.
This connecting member is constituted of the adhesive agent containing a predetermined amount of conductive material such as conductive particles and so on. This connecting member is disposed between each of protruding electrodes of an electronic part and a conductive pattern of a printed wiring board. By applying a pressure or heating with a pressure, the electrodes on both the parts are electrically connected to each other and electrodes formed adjacent each other of the same are provided with an electrical insulation. As a result, the protruding electrodes of the electronic part and the conductive pattern of the printed wiring board are bonded to each other and fixed.
A basic concept for making the above connecting member correspond to the fine pitch is that an insulation between adjacent electrodes is secured by making a diameter of each of conductive particles smaller than the insulating portion between the adjacent electrodes, the containing amount of the conductive particles is set to such an extent that the particles do not contact each other and conductivity of the connecting portion is obtained by making the conductive particles exist securely on the electrodes.
If the diameter of the conductive particle is reduced according to the above conventional method, however, an area of the conductive particle"" surface increases remarkably so that a secondary cohesion occurs, thereby combining adjacent particles with each other. As a result, the insulation between the adjacent electrodes cannot be maintained. If the containing amount of the conductive particles decreases, the number of the conductive particles on electrodes to be connected also decreases so that the number of contacting points becomes short. As a result, the conduction between the connecting electrodes cannot be obtained. Consequently, it is difficult to make the connecting member correspond to fine pitch while a long term connecting reliability is maintained.
That is, by a remarkable correspondence to the fine pitch trend, miniaturization of an electrode area and a gap (space) between adjacent electrodes have progressed, so that the conductive particles on the electrodes flows out between the adjacent electrodes with adhesive agent because of pressurization at the time of connection or heating with a pressure.
To solve such a problem, conventionally, a connecting member in which by coating the conductive particles for insulation, a quantity of the conductive particles in the connecting member is increased and a connecting member constituted of an adhesive layer containing the conductive particles and a layer not containing them have been proposed.
FIGS. 1 and 2 show these conventional connecting members.
In case where an object is a glass substrate 200 as shown in FIG. 1, flatness of a mounting region for an IC (integrated circuit) 201 in glass substrate 200 is about xc2x10.5 xcexcm and if in protruding electrodes 202 of the IC 201, there is few deflection (about xc2x10.5 xcexcm) in the height of each protruding electrode like a gold plated bump, it is possible to electrically connect the wiring pattern 203 of the glass substrate 200 to the protruding electrodes 202 of the IC 201 through conductive particles 205 contained in a connecting member 204.
Because each of the parts such as the ICs is flat, if the thickness of the connecting member 204 is a height of the protruding electrode 202 of the IC 201 (ordinarily, about 15-25 xcexcm and ITO pattern wired on a glass is some Angstrom) about xc2x15 xcexcm, the connecting member 204 is charged securely under the IC 201. Therefore, the connecting member 204 does not have to be made thicker than necessary and at the stage of temporary pressure-fitting (pressurization) of an initial period of mounting, the conductive particles 205 can be nipped between the wiring pattern 203 on the glass substrate 200 and the protruding electrodes 202 of the IC 201. After that, even if the binder of the connecting member flows out at the time of pressure-fitting (heating with a pressure), the nipped conductive particles 205 do not flow out, so that when the connecting member is hardened, an electrical connection is established between the wiring pattern 203 on the glass substrate 200 and the protruding electrode 202 of the IC 201 through the conductive particles 205.
In FIG. 1(A), the connecting member 204 (for example, anisotropic conductive film: ACF) is bonded to the glass substrate 200. Usually, the anisotropic conductive film is bonded onto the glass substrate 200 by carrying out ordinary heating with a pressure (heating with a pressure is performed at a pressure of about 100 N/cm2 and a heating temperature of 70-100xc2x0 C.). With this state, positioning between the wiring pattern 203 of the glass substrate 200 and the protruding electrode 202 of the IC 201 is carried out.
In FIG. 1(B), the IC 201 is temporarily press-fit to the glass substrate 200. The temporary press-fitting of the IC 201 is carried out by only a pressure or heating with a pressure (heating temperature is about 70-100xc2x0 C.).
In FIG. 1(C), the IC 201 is finally press-fit to the glass substrate 200. The final press-fitting of the IC 201 is carried out by heating with a pressure. Because a temperature at this time is higher than the glass transition temperature of the anisotropic conductive film, a flow of the binder occurs. At this time, the conductive particles 205 nipped between the protruding electrode 202 of the IC 201 and the wiring pattern 203 of the glass substrate 200 does not flow, but the other conductive particles 205 flow.
FIG. 1(D) shows a state in which the anisotropic conductive film is hardened. If heating with a pressure is carried out in the final press-fitting, after resin flows, it is hardened. This series of the above described processes is the connecting process.
However, if the object is not a glass substrate but a printed wiring board 300 as shown in FIG. 2, a deflection (xc2x1 several xcexcm) may be generated in the height of the wiring pattern 303 or a deflection (xc2x1 several xcexcm) may be generated in the height of the protruding electrode 202 of the IC 201 like a gold wire bump. In this case, if the thickness of the connecting member 204 is height of the wiring pattern 303 of the printed wiring board 300 (about 20 xcexcm) plus height of the protruding electrode of the IC (about 20 xcexcm), it is necessary to add 10-20 xcexcm to the above thickness by considering the safety.
In this case, because the thickness of the connecting member 204 is large at the stage of temporary press-fitting (pressurization) of the initial period of mounting, the conductive particles 205 cannot be nipped between the wiring pattern 303 of the printed wiring board 300 and the protruding electrode 202 of the IC 201. After that, when the binder of the connecting member 204 flows at the time of final press-fitting (heating with a pressure), the conductive particles 205 also flow. When the gap between the wiring pattern 303 of the printed wiring board 300 and the protruding electrode 202 of the IC 201 coincides with the size of each of the conductive particles 205, the flowing conductive particles 205 are nipped therebetween. However, the conductive particles 205 are not concerned with every connection. Therefore, electrical connection will not be secured. Alternatively, as it is necessary to obtain parts having a strict specification, cost is increased.
FIG. 2(A) shows a state in which the connecting member 204 (for example, anisotropic conductive film) is bonded to the printed wiring board 300. The anisotropic conductive film is pasted onto the printed wiring board 300 by normal heating with a pressure (this heating with a pressure is carried out at a pressure of about 100 N/cm2 and a heating temperature of about 70-100xc2x0 C.). In this state, positioning of the wiring pattern 303 of the printed wiring board 300 and the protruding electrode 202 of the IC 201 is carried out.
FIG. 2(B) shows a state in which the IC 201 is temporarily press-fit to the printed wiring board 300. The temporary press-fitting for the IC 201 is carried out by only pressurization or heating with a pressure (heating temperature is about 70-100xc2x0 C.).
FIG. 2(C) shows a state in which the IC 201 is finally press-fit to the printed wiring board 300. The final press-fitting of the IC 201 is carried out by heating with a pressure, and because the temperature at this time is higher than the glass transition temperature of the anisotropic conductive film, the binder flows. Because at this time, no conductive particles 205 are nipped between the protruding electrodes 202 of the IC 201 and the wiring pattern 303 of the printed wiring board 300, all the conductive particles 205 flow. Thus, when the gap between the wiring pattern 303 of the printed wiring board 300 and the protruding electrode 202 of the IC 201 coincides with the diameter of the conductive particle 205, the flowing conductive particles 205 to the gap are nipped therebetween. Therefore, the conductive particles 205 do not exist in every gap between the wiring pattern and protruding electrode.
FIG. 2(D) shows a state in which the anisotropic conductive film is hardened. If heating with a pressure is carried out in the final press-fitting, resin is hardened after a flow. The series of these steps is a connecting process.
Therefore, if electrical connection via the conductive particles is achieved regardless of a slight unevenness of the printed wiring board which is an object and a slight unevenness of the protruding electrode of the IC, it can be considered that a reliability sufficient for practical use can be obtained even on a printed wiring board whose cost is suppressed.
Accordingly, the present invention has been achieved in views of the above problems, and therefore, it is an object of the invention to provide an electrical connecting member and electrical connecting method capable of achieving electrical connection via conductive particles regardless of a slight unevenness of an object material.
To achieve the above object, according to a first aspect of the present invention, there is provided an electrical connecting device for electrically connecting an electrical connecting portion of a first object to an electrical connecting portion of a second object, the electrical connecting device comprising a film-like adhesive layer to be disposed on the first object and constituted of a plurality of conductive particles and a binder containing the conductive particles; and paste disposed on the film-like adhesive layer and having a fluidity.
According to the first aspect of the invention, the film-like adhesive layer and paste are possessed to achieve electrical connection between the electrical connecting portion of the first object and the electrical connecting portion of the second object.
The film-like adhesive layer is an adhesive layer to be disposed on the first object and constituted of a plurality of conductive particles and a binder containing the conductive particles. The paste is disposed on the film-like adhesive layer and has a fluidity.
Thus, only by disposing the film-like adhesive layer on the first object and then paste on the film-like adhesive layer, in the electrical connecting portions of the first and second objects, the paste having a fluidity is nipped between the first object and second object and flows, so that the conductive particles in the film-like adhesive layer are not moved but only the paste flows. Therefore, regardless of a slight unevenness in the first object, the first object and second object can be closely fit to each other, and the electrical connecting portion of the first object can be electrically connected to the electrical connecting portion of the second object positively by using the conductive particles in the film-like adhesive layer.
Preferably, according to a second aspect of the present invention, each of the conductive particles has an almost uniform diameter. According to a third aspect of the present invention, preferably, the material of the paste is the same adhesive agent as the material of the binder of the film-like adhesive layer.
As a result, when the paste and the binder in the film-like adhesive layer are heated with a pressure, they react therewith so as to affix the first object and second object to each other. Because the conductive particles have almost uniform diameter, the electrical connecting portion of the first object can be connected to the electrical connecting portion of the second object securely such that they positively nip the conductive particles therebetween and are not floated.
According to a fourth aspect of the present invention, preferably, the thickness of the film-like adhesive layer is set almost equal to or larger than the diameter of each of the conductive particles.
As a result, a case in which any conductive particle projects from the film-like adhesive layer is eliminated.
According to a fifth aspect of the present invention, preferably, the viscosity of the paste is set to be smaller than the viscosity of the film-like adhesive layer.
As a result, the paste flows with a precedence in a gap between the first object and second object and hence the film-like adhesive layer is not moved, thereby making it possible to hold the conductive particles firmly thereat.
According to a sixth aspect of the present invention, preferably, the electrical connecting portion of the first object is a wiring pattern on a circuit substrate, the electrical connecting portion of the second object is an protruding electrode of an electronic part and the conductive particles in the film-like adhesive layer electrically connects the wiring pattern of the circuit substrate to the protruding electrodes of the electronic part.
As a result, the wiring pattern of the circuit substrate and the protruding electrodes of the electronic part can be electrically connected to each other by using the conductive particles in the film-like adhesive layer.
According to the third aspect of the present invention, a melting temperature of the paste is preferably set lower than the melting temperature of the film-like adhesive layer.
According to a seventh aspect of the present invention, there is provided an electrical connecting method for electrically connecting an electrical connecting portion of a first object to an electrical connecting portion of a second object, the electrical connecting method comprising the steps of: adhesive layer allocation step for allocating a film-like adhesive layer constituted of a plurality of conductive particles and a binder containing the conductive particles on the electrical connecting portion of the first object; paste allocation step for allocating paste having fluidity on the film-like adhesive layer; and connecting step for heating with a pressure for electrically connecting the electrical connecting portion of the first object to the electrical connecting portion of the second object through the conductive particles in the film-like adhesive layer.
According to the seventh aspect of the invention, at the adhesive layer allocation step, the film-like adhesive layer constituted of a plurality of the conductive particles and a binder containing the conductive particles is disposed on the electrical connecting portion of the first object.
At the paste allocation step, the paste having the fluidity is disposed on the film-like adhesive layer.
At the connecting step, heating with a pressure is carried out to electrically connect the electrical connecting portion of the first object to the electrical connecting portion of the second object by the conductive particles in the film-like adhesive layer.
As a result, only by disposing the film-like adhesive layer on the first object and then paste on the film-like adhesive layer, in the electrical connecting portions of the first and second objects, the paste having the fluidity is nipped between the first object and second object and flows. Thus, because only the paste flows while the conductive particles in the film-like adhesive layer are not moved, the first object and second object can be closely fit to each other even if there is slight unevenness in the first object, so that the electrical connecting portion of the first object can be electrically connected to the electrical connecting portion of the second object surely by using the conductive particles in the film-like adhesive layer.
According to an eighth aspect of the present invention, preferably, the connecting step comprises a first pressure heating step for heating at a temperature below a glass transition temperature of a binder and paste with a pressure; and a second pressure heating step for heating at a temperature above the glass transition temperature of the binder and paste with a pressure.
As a result, because the binder and paste are heated at a temperature below the glass transition temperature at the first pressure heating step, they are hardened only temporarily.
Because at the second pressure heating step, the binder and paste are heated with a pressure at a temperature higher than the glass transition temperature of the binder and paste, the binder and paste are hardened completely.
According to a ninth aspect of the present invention, preferably, the binder and paste are of the same or almost equal component.
According to an eleventh aspect of the present invention, preferably, the connecting step comprises a first pressure heating step for heating at a temperature below the melting temperature of the binder and above the melting temperature of the paste with a pressure; and thereafter a second pressure heating step for heating at a temperature above a reaction starting temperature of the binder and paste with a pressure.